Ed- you're right. For example, look at the two subs. Assuming they are of the same class, the newer one (with the higher hull number) has a curved piece forwards of the sail, where it meets the hull. The older sub does not have this. It's probably to further quieten the sound as the sub moves thru the water. This would have been nice-to-know information during the cold war. BTW I was in VS-22, attached to the Saratoga.